[PATCH 01/20] drm/amd/display: Determine DRM connector type more accurately

[Timur Kristóf]

On Wed, 2025-08-06 at 14:13 -0400, Harry Wentland wrote:
> 
> 
> On 2025-08-06 13:45, Timur Kristóf wrote:
> > 
> > Harry Wentland
> > <harry.wentland at amd.com <mailto:harry.wentland at amd.com>> ezt írta
> > (időpont: 2025. aug. 6., Sze 16:56):
> > 
> >     this patch regresses the kms_bw IGT test with Navi 31 and 48
> >     with a single 4k60 DP display connected. These subtests fail
> >     when they should pass:
> > 
> >     linear-tiling-2-displays-1920x1080p
> >     linear-tiling-2-displays-2160x1440p
> >     linear-tiling-2-displays-2560x1440p
> >     linear-tiling-2-displays-3840x2160p
> >     linear-tiling-3-displays-1920x1080p
> >     linear-tiling-3-displays-2160x1440p
> >     linear-tiling-3-displays-2560x1440p
> >     linear-tiling-3-displays-3840x2160p
> >     linear-tiling-4-displays-1920x1080p
> >     linear-tiling-4-displays-2160x1440p
> >     linear-tiling-4-displays-2560x1440p
> >     linear-tiling-4-displays-3840x2160p
> > 
> >     We confirmed with a revert of this patch.
> > 
> >     Harry
> 
> > At the moment I don't see what is there that would make a
> > difference to Navi 31 or 48.
> > 
> 
> Not sure either. But that's why we have these tests because
> they often catch things that aren't obvious.
> 
> Harry

Hi Harry,

I took a look at this issue.

I found the code for this igt test here:
https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/tests/kms_bw.c?ref_type=heads

It seems to me that the test sets up a very simple display scenario and
tries to check that the CRC isn't zero.

However, the variable "igt_crc_t zero" is never initialized (and is
also of the wrong type). So what the test is actually doing is
comparing the "captured" CRC with a piece of uninitialized memory.

That being said, I decided to rewrite my patch and only check the DC
connector type for DVI signals to distinguish between DVI-D and DVI-I
specifically, and otherwise leave the rest of the code as-is in order
to avoid any potential regressions.

Does that sound OK to you?

Thanks & best regards,
Timur